It is often required to convey additional data, such as “metadata”, along with a stream of digital audio. The most convenient and reliable way to do this is to “bury” the additional data into the audio stream itself, since separately-carried data often gets lost.
An elementary way to bury data is to replace the least-significant-bit of an audio data word in a Pulse Code Modulation (PCM) stream by a bit of the additional data stream. This is not recommendable as an audiophile procedure, however, as it results in undithered truncation of the audio data word and the insertion of noise which may contain tones if the additional data stream contains repeating patterns.
More sophisticated approaches are discussed in the paper “A High-Rate Buried-Data Channel for Audio CD” by Gerzon, Michael A. and Craven, Peter G., J. Audio Eng. Soc. Volume 43 Number 1/2 pp. 3-22; January/February 1995. However, prior art methods of burying data have resulted in a loss of audio quality which, although small, may be unacceptable in circumstances where “lossless” or bit-exact transmission of a digital audio signal is demanded.
It is intrinsic that a stream that conveys additional data is different from an original stream from which it was derived. However, it might be possible to recover the original stream if the data could be buried in a way such that a special decoder is able to recover the original digits exactly. Accordingly, there is a need for improved encoding and decoding techniques, which can better retain the original audio quality.